Antenna array



April 19, 1955 Filed July 31, 1952 R. H. Du HAMEL 2,706,780

ANTENNA ARRAY 2 Sheets-Sheet l i 5 -4/2 MWA/i mrs/5 fia/Mimi amm/WINI/ENTOR.

RaYMrJND H. Du HEMEL.

TTORNEY April 19, 1955 R. H. DU HAMEL 2,706,780

ANTENNA ARRAY IN IEN TOR.

RHYMUND H. DUHAMEL B, M AM ATTORNEY N. LA?

United States Patent O ANTENNA ARRAY Raymond Horace Du Hamel,Lawrenceville, N. J., as-

signor to Radio Corporation of America, a corporation of DelawareApplication July 31, 1952, serial No. 301,891

The terminal fifteen years of the term of the patent to be granted hasbeen disclaimed 12 Claims. (Cl. Z50-33.53)

This invention relates to antennas and particularly to antenna arrays inwhich the field pattern is shaped to provide a desired patterncharacteristic.

In the development of broadcasting services, antennas which aredirectional, as well as antennas which are omnidirectional in theazimuthal plane, have been employed. The generation of large amounts ofradio frequency power at ultrahigh frequencies is not, at the presentstate of the art, as efficient or economical as is desired. Antennasystems heretofore used at frequencies up to 300 megacycles are notsufliciently efficient themselves to recommend them for widespread useas broadcast antennas for ultrahigh frequency signals. The problem istherefore presented in ultrahigh frequency television broadcasting, forexample, as to how most efficiently and economically to use radiofrequency energy in the range from 470 to 890 megacycles.

For the most economical use of the avaliable radio frequency energy, theradiated field intensity throughout the primary service area of thebroadcasting establishment should be as constant as possible. Aspecially shaped vertical radiation pattern may be used to obtain asubstantially constant field strength over the primary service area ofan ultrahigh frequency broadcasting installation.

The present invent-ion is directed to antenna arrays in which the fieldpattern characteristic can be shaped to provide a desired field patternwith extremely low radiation loss due to energy being wasted inundesired directions. Antenna arrays in accordance with the inventionmay be built to present a w-ide variety of field patterns, but it isexpected that an important application thereof will be for ultrahighfrequency broadcasting services utilizing horizontal polarization toprovide maximum coverage of the broadcast service area.

An object of this invention is to provide an antenna array of simplephysical arrangement capable of producing specially shaped field patterncharacteristics.

Another object of this invention is to provide an antenna array capableof producing a shaped beam radiation pattern characteristic which makesuse of a straightforward and uncomplicated transmission line couplingarrangement.

A further object of this invention is to provide an antenna array forhorizontally polarized waves in which the vertical radiation pattern maybe simply controlled by the physical shape of the array.

Yet another object of this invention is to provide a new method ofdesigning an antenna array to produce a specitied radiation pattern.

Still another object of this invention is to simplify design methods ofantenna arrays to produce a specified field pattern.

In accordance with the present invention, these and other objects areattained by an antenna array which includes a plurality of antennaelements closely spaced to a current sheet reflector structure. All ofthe currents in the antenna elements are made equal and in phase byarranging the transmission line connections s`o that each element iscoupled through a quarter-wave of line to a common voltage point. Theamount that each of the antenna elements in the array contributes to thefield pattern characteristic -is determined and controlled by thespacings of the individual antenna elements from the current sheetreector structure. The effective phase of the currents in the individualantenna elements relative to a far field point is controlled bydcviating or warping the sheet refiector from a linear reference base.The spacing "ice between the -individual antenna elements and thereflector sheet may vary from one-quarter wavelength to as little as1/100 of a wavelength. In general, the warping of the sheet reflector atany point along the array relative to the linear base reference will beless than one-half wavelength, although greater variation in the reectorsheet is contemplated under certain conditions. The resultant arrayproduces a field pattern characteristic which is simply controlled byphysical adjustments of the shape of the antenna array itself, and theantenna coupling networks are kept very simple.

A more detailed explanation follows in conjunction with the accompanyingdrawings, in which:

Fig. l is an elevation of an array of antenna elements in front of acurrent sheet reflector, embodying the principles of this invention;

Figs. 2 and 3 are curves explanatory of certain features of theinvention;

Fig. 4 is an elevation of another antenna array in accordance with theinvention;

Fig. 5 is an elevation of an antenna array, in accordance with thisinvention, which has an omnidirectional pattern in the horizontal planeand a shaped vertical pattern characteristic;

`gig. 6 is a cross section along the line 6 of Fig. 5; an

Fig. 7 is a cross section along the line 7 of Fig. 5.

Referring now to Fig. l, a plurality of antenna elements 11a through 11pare arranged in close proximity to a current sheet reiiector 13. For thepurpose of this discussion, the antenna elements 11a through 11p areassumed to be identical elements in which the currents are parallel tothe sheet reflector 13. Simple half-wave dipoles may be utilized as theantenna elements 11a through 11p, although it should be understood thatsimple dipoles of other lengths, folded dipoles, unipoles, full-waveloops parallel to the sheet reflector, and certain continuous wirearrays may also be employed. The current sheet reflector 13 may be ofsolid metallic or conductive material, or may consist of a conductivescreen; or a grid or network of conductors may be used to approximate asolid sheet reflector.

Each of the plurality of antenna elements 11a through 11p Iis coupled toa transmission line network having a main transmission line 15 and aplurality of quarter-wave coupling lines 17a through 17p. Thetransmission lines 15 and 17 are indicated by a single line on thedrawing. This representation is intended to be schematic, and includesas well transmission lines having either single or plural conductors,such as waveguides, coaxial lines and parallel wire lines.

All of the antenna elements 11a through 11p in the array are fed withequal and in-phase currents. The transmiss-ion line connection systemshown in Fig. l is arranged to produce equal in-phase currents in all ofthe antenna elements 11a through 11p as follows: The current feed pointof each antenna element 11a through 11p is coupled through an oddquarter-wavelength coupling line 17a through 17p to an equal andin-phase source of voltage. The length of the coupling lines 17 isselected as an odd multiple of a quarter-wavelength since thereceiving-end current of a line having a length equal t0 is independentof terminating end impedances and is determined by the sending-endvoltage.

By connecting the odd quarter-wavelength coupling lines 17 at multiplesof a wavelength in electrical distance along the transmission line 15,equal and in-phase voltages are impressed across the quarter-wavelengthcoupling lines 17 yielding equal currents in the identical antennaelements 11a through 11p. It will be apparent to those skilled in theantenna art that the spacing of the antenna elements along the line ofthe array may be any integral number of half-wavelengths in electricaldistance along the transmission line 15 for such a coupling arrangement.For odd multiples of a half-wavelength, such as one-half or three-halveswavelength spacing, the connection of the quarter-wave coupling line 17hassociated with any one antenna element, 11h., for example, will becoupled in opposite sense across the transmission line to that of a nextadjacent coupling line 17g or 171'. As shown in Fig. 1 of the drawing,however, each of the quarter-wave couat any point, the current sheetreflector 13 is shaped so that i/ Qitio 1) pling lines 17 will beconnected in the saine sense 'across 5 the equal voltage points on themain transmission line 15. Wngre WX) is the required pnn-Se VariationOther simple coupling networksto feed all of the an- The antennaelements 11a through 11p are spaced eml'fl 1U1I1t5-11 through 111? Wlhequal CUFFEHS may from the current sheet reiiector 13 a distance suchthat readily be devised. An equal-length branching system like the oneshown in connection with Fig. 4 may also be 10 RUIM) :sin (Zlsn) (2)employed. A

The field pattern in a plane perpendicular to the aritenna elements 11athrough 11p is controlled by the where X is the distance measured fromthe center of physical shape of the array. Knowing the desired eld theaperture of the array to any element and Xp. i s pattern and theaperture of the array, it is relatively the distance to the position ofthe pth element, Sp is simple to calculate the current distributionacross the the spacing of the element from the current sheet regivenaperture required to produce the desired pattern. ector 13 and R (Xn) isthe normalized magnitude This required current distribution across theaperture ot of the current I as Xn. the array will have certain valuesof magntiudc and The curves of Figs 2 and 3 illustrate currentmagniphase. In this invention, the effective magnitude of the 20 tudeand p hase distribution across an antenna array havfield from eachantenna element 11a through 11p is proing a vertical aperture of tenwavelengths to secure a portional to the sine of the spacing in radiansof the good approximation of a cosecant squared vertical patantennaelement 11a through 11p from the current sheet tern characteristic.reiicctor 13. The effective phase of the field from each The followingtable is representative of the dimensions element is proportional to thedisplacement from a linear of a unidirectional antenna array having alinear aperbase reference line 19 of the current sheet reflector 13 tureof ten wavelengths with sixteen dipole antenna elenear the element inquestion. ments in front of a conductive current sheet reector. lt mightappear to the Worker in the art that a plane The absolute values ofcurrent for theldipole element reflector can be utilized in which thecurrent magnitude positions chosen represent those s hown in Fig. 2. Theacross the aperture of the array is controlled by the spacphasevariation 1]/(X) for. the distance of the current ing of the antennaelements from a sheet reflector, and sheet reflector from the linearbase reference is taken at the same timeasimple transmission linenetwork used to from the .curve ot Fig. 3. The spacings of each of theproduce the required phase distribution function. Such elements in thesixteen element array in centimeters is an arrangement gives rise to aserious design problem. given for a midband frequency of 940 megacycles.

W-ave' \Torrnal 3 i in Antenna lengths Absolute ed Clu ilpcn PhaseElement from Current rent Ma` Spacing meter' Phase Deviation v0./2center Magari mtudeg' s/,rx go fn i (X) in wave- Dipole) oi Ariay tudc R(Xu) s# lengths Y 41%@ .5s .31 .07s 2. 50 171 475 41m. 70 .32 .030 2. 55155 431 3746 .75 .34 .035 2. 72 139 380 21` .s1 .37 .093 2. 97 123 3422%, 92 .42 .105 3. 36 104 290 1916 1.0s .49 122 3. 97 30 233 UAG 1.4 .04.i0 5.11 65 -l- 130 /i 2.2 1.0 .25 8 42 115 ai@ 2.2 1.0 .25 s 42 .11315A@ 1.4 .04 .i0 5.11 55 .180 1%. 1. 03 .49 .122 3. 97 36 23s 2%; .92.42 .105 3.30 104 .290 21%; .si .37 .093 2.97 123 .342 3%6 .75 .34 .0852.72 130 .335 4145 .70 .32 .030 2.55 155 .431 411/15 .6s .3i .073 2, 50171 .475

lf the transmission lines from points of equal voltage are varied inlength to alter the phase of the current in the individual antennaelements, then the transmission line connection system Will no longerproducel equal currents in all of the antenna elements and the effectivecurrent magnitude across the aperture will be altered. Such anarrangement therefore is subject to interaction between the adjustmentsof current magnitude and phase, and the design of sufliciently isolatedtransmission line coupling circuits capable of some degree of adjustmentto duplicate the action of the preferred arrangement of the presentinvention becomes extremely complicated and tedious.

Referring now to Figs. 2 and 3 as well as to Fig. l, let it be assumedthat the required phase and magnitude of the current distribution havebeen determined. Fig. 2 illustrates a representative desired currentmagnitude distribution across an aperture having a length L. Theaperture of an antenna is used in this specification to denote theequivalent area over which the antenna interchanges energy with freespace. Fig. 3 is illustrative of a desired phase ol' the current acrossthe same aperture of length L relative to a far field point. lt isconvenient for analytical purposes, although not necessary, to use theconcept of a continuous Current distribution across the entire aperturelength L.

The current sheet rellector 13 of the antenna array is shaped or warpedwith respect to the linear base reference i9 according to the phasecurve shown in Fig. 3. Let Y represent the distance from the linear basereference 19 to the surface of the current sheet reflector i3 In Fig. 4there is shown an alternative feeding arrangement for an antenna arrayin accordance with this invention. T o insure that all of the antennaelements 11a through 11p are supplied with equal current, they arecoupled by means of odd quarter-wavelength coupling lines 17a through17p to points of equal voltage 21 with respect to the remainder of thetransmission line system.

The points of equal voltage 21 are formed by a transmission linebranching system. A main transmission line 23 from the radio frequencyapparatus 24 (such as a transmitter or receiver), to which the antennasystem is to be coupled, has a iirst branching point 2S. From this firstbranching point 2S, a plurality of equallength transmission lines 27extends to secondary branching points 29. From each of these secondarybranching points 29 a plurality of also equal-length transmission lines31 extend to the points of equal voltage 21.

For optimum operation, the transmission line coupling network should bearranged so that the equal length transmission lines 27 between thefirst branching point 25 and secondary branching points 29 are anintegral multiple of half-wavelengths long, and the equal-lengthconnection lines between the secondary branching points 29 and thepoints of equal voltage 21 are also selected to be some integralmultiple of half-wavelengths long at the operating frequency. Byselecting the first set of equal-length transmission lines 27 to be anintegral number of half-wavelengths and the second set of equal-lengthtransmission lines 31 to be also some integral number ofhalf-wavelengths (of course, not necessarily the same number ofhalf-wavelengths as that for the first set of equal-length transmissionlines 27), the transmission line interconnection system presents equalvoltage points at every branching point 25, 29 as well as the points ofequal voltage 21.

With the arrangement just described, if the antenna is used as atransmitting antenna, whatever voltage is impressed across the firstbranching point 25 by the radio frequency apparatus 24 (in this case, atransmitter) will also appear across each of the points of equal voltage21 to which the antenna elements 11a through 11p are coupled by the oddquarter-wavelength coupling lines 17a through 17p. The antenna elements11a through 11p are therefore all excited with equal and in-phasecurrents.

The arrangement shown in Figs. 5, 6 and 7 has eight arrays similar tothat described above in connection with Figs. 1, 2 and 3 spaced around apolygonal structure. This array has an omnidirectional pattern in thehorizontal plane and a cosecant squared vertical pattern characteristic.The separate faces 13a through 13h perform the same function and areeach similar to the single sheet reflector 13 of Fig. 1. Each of theseveral refiector faces 13a through 13h is deviated from a linear basereference in the same manner as the current sheet reflector 13 of Fig. 1to control the effective phase of the field dueto each antenna element11a through 11p. The amount of deviation from the linear base referencefor each of the several reflector faces 13a through 13h is in accordancewith the curves shown in Fig. 3 and described above. The linear basereference itself is referred to a vertical plane through the smallestdimension of the reector face, and in this instance is tilted upward by5.7 degrees to bring the maximum radiation for the particular arrayshown to have a downward tilt of 1.3 degrees from the horizontal.

A comparison of the spacing Sa of the antenna elements 11 from therefiector sides 13a through 13h in Fig. 5 shows a representativevariation in such spacing for an array to achieve a cosecant squaredvertical pattern power distribution characteristic. The spacing of theindividual elements 11 along each of the single reflector faces (forexample, 13C) is in accordance with the table given above in thedescription of Figs. l, 2 and 3.

By referring to Fig. 6, it may be seen that the perpendicular distancebetween any two opposite reector sides (for example, 13C and 13g) may beof the order of Ak at the top of the array for an embodiment having anoctagonal cross section; and near the bottom of the array, as shown inFig. 7, the cross-sectional dimension between the same two reiiectorsides is of the order of a wavelength. With such dimensions, the lengthof the sides of the polygon at the narrowest portion of the arraybecomes less than one-half wavelength. It is therefore necessary undercertain conditions, like the one herein described, to make theindividual antenna elements 11 shorter than one-half wavelength so thatthe sector occupied thereby will not overlap an adjacent sector.Normally, the spacing between the centers of adjacent dipole antennaelements 11 in a single layer like that shown in Fig. 6, will varybetween 3/sx and SAM for an eight-sided array.

In the example shown, the spacing between the centers of adjacentantenna elements 11 in an upper layer as shown in Fig. 6 will be .55}\,while the spacing of similar elements in a lower layer like that of Fig.7 will be .39)\. As was mentioned above, all of the antenna elements arepreferably identical and will therefore be of the order of 1A to 3A;wavelengths in length.

It will, of course, be apparent that if the number of sides of thepolygon is increased to l0, l2 or 14, there will be less variation incross-sectional dimensions between upper and lower layers, and theindividual antenna elements 11 may be made longer and still achieve anadditive field relative to some far field point from two adjacentradiating elements in a single layer.

The cross-sectional configuration of the closed figure approachescircularity as the number of sides is increased. The sheet refiectorstructure may be in fact made circular in cross section without changingthe vertical pattern characteristic and without detrimental effects onthe horizontal circularity where the minimum diameter of the figure thusformed is of the order of a wavelength or more.

All of the antenna elements in a longitudinal sector, like thoseassociated with a single refiector face, 13c for example, in Fig. 5 arecoupled by a simple transmission line network to a common voltage pointas explained in conjunction with Figs. 1 and 4. Such networks areomitted from the drawing in Figs. 5, 6 and 7 for the sake of a clearershowing. All of the elements in the several sectors may be coupled to acommon transmission line network, if the entire omnidirectional array iscoupled in phase to the associated radio frequency apparatus, or anetwork individual to each sector (or oppositely disposed sectors) isnecessary for phase rotational coupling, commonly called turnstilefeeding.

Unidirectional antenna arrays having a cosine distribution pattern inthe horizontal plane like those shown in Figs. l and 4 have furtherapplication in laboratory or experimental uses. Such directional arraysare especially convenient for pattern synthesis or analysis of broadsidearrays. Since the antenna array of this invention provides separate andnon-interacting physical adjustments of both the current magnitude andphase relative to a far field point, a desired pattern characteristicmay be obtained by a trial and error method. Also, a calculated currentand phase distribution across an aperture to produce a certain patternmay be verified experimentally by actual pattern measurements veryrapidly and with extremely simple physical equipment. The number andcomplexity of the required physical adjustments for such patternsynthesis and verification are materially reduced over prior systems.Furthermore, the results obtained from an experimental verificationusing an antenna in accordance with this invention more nearly representthe actual pattern characteristic conditions than can be obtained bymathematical solution either manually or by pattern calculating devices.

What is claimed is:

l. An antenna array comprising a conductive sheet reflector and aplurality of antenna elements closely spaced to said sheet reflector,said sheet reflector being warped from a straight linear reference baseextending along the length of the aperture of said antenna to controlthe effective phase of the field pattern characteristic due to each ofsaid antenna elements relative to a far field point, the spacing of saidelements from said reflector surface varying across the aperture of saidarray in. accordance with the relative magnitude of the field due to theindivid ual elements in the array with respect to a far field point.

2. An antenna array comprising a plurality of antenna elementsdistributed across an aperture, a current sheet reflector structure inthe near zone of said plurality of elements, said current sheetreiiector structure having a warped spatial deviation from a straightbase reference line extending along the length of said aperture, saiddeviation varying therealong according to a required phasecharacteristic, said antenna elements being spaced from said currentsheet reflector by different amounts in direct proportion to a desiredcurrent distribution across said aperture.

3. An antenna as defined in claim 2 wherein said spaced antenna elementsare dipoles.

4. An antenna array comprising a plurality of antenna elementsdistributed across an aperture, a current sheet reflector structure inthe near zone of said plurality of elements, said current sheetreflector structure having a spatial deviation from a straight basereference line extending along the length of said aperture, varyingaccording to a required phase characteristic, said antenna elementsbeing spaced from said current sheet reflector by different amounts indirect proportion to a desired current distribution across saidaperture, and a transmission line coupling network connected to saidantenna elements to couple in equal degree to each of said elementswhereby equal instantaneous currents are produced in all of said antennaelements.

5. An antenna array comprising a plurality of antenna elementsdistributed across an aperture, a current Vsheet reflector structure inthe near zone of said plural- 6. An antenna array comprising a pluralityof antenna elements distributed across an aperture, a current sheetreflector structure in the near zone of said plurality of elements, saidcurrent sheet reflector structure having a spatial deviation from astraight base reference line along the length of said aperture varyingaccording to a required phase characteristic, said antenna elementsbeing spaced from said current sheet reflector by different amounts indirect proportion to a desired current distribution across saidaperture, and transmission line coupling means for feeding each of saidelements from a common voltage reference point through a transmissionline having a length of an odd multiple including unity of one-quarterwavelength at the operating frequency.

7. An antenna array comprising a plurality of antenna elementsdistributed along an aperture of several wavelengths, a continuoussurface conduction current sheet reflector in the near zone of saidplurality of elements, said current sheet reflector being spaced from astraight base reference along the length of said aperture by an amountwhich varies directly in free space wavelengths as a required phasecharacteristic of current in said elements across said aperture, saidantenna elements being spaced from said current sheet reflector bydifferent amounts each in direct proportion to a desired currentmagnitude distribution characteristic along the length of said aperture.

8. An antenna array comprising a plurality of antenna elementsdistributed along an aperture of several wavelengths, a continuoussurface conduction current sheet reflector in the near zone of saidplurality of elements, said current sheet reflector being spaced from astraight base reference line along the length of said aperture by anamount which varies directly in free space wavelengths as a requiredphase characteristic of current in said elements across said aperture,said antenna elements being spaced from said current sheet reflector bydifferent amounts each in direct proportion to a desired currentmagnitude distribution characteristic along the length of said aperture,and transmission line coupling means for feeding each of said elementsfrom a common voltage reference point through a transmission line havinga length of an odd multiple including unity of onequarter wavelength atthe operating frequency.

9. An omnidirectional antenna array comprising a plurality of conductivesheet reflector structures forming the sides of a closed polygon, eachof said plurality of conductive sheet reilector structures having aplurality of antenna elements closely spaced thereto, each of saidplurality of conductive sheet reflectors being deviated in free spacewavelengths from a linear reference base eX- tending along the length ofthe aperture of said antenna in direct proportionto a predeterminedphase characteristic, the antenna elements associated with each of saidplurality of reflector structures being spaced therefrom by differentamounts along the length thereof in direct proportion to a predeterminedcurrent distribution across said aperture.

10. An omnidirectional antenna array comprising a plurality ofconductive sheet reflector structures forming the sides of a closedpolygon, each of said plurality of conductive sheet reflector structureshaving a plurality of antenna elements closely spaced thereto, each ofsaid plurality of conductive sheet reflectors being deviated in freespace wavelengths from a linear reference base extending along thelength of the aperture of said antenna in direct proportion to apredetermined phase characteristic, the antenna elements associated witheach of said plurality of reflector structures being spaced therefrom bydifferent amounts along the length thereof in direct proportion to apredetermined current distribution across said aperture, and a pluralityof transmission line coupling networks, each of said networks beingindividual to all of said elements associated with one of said reflectorstructures and feeding each of said elements associated with saidreflector structure from a common voltage reference point through asection of transmission line having a length of an odd multipleincluding unity of one-quarter wavelength at the operating frequency.

1l. An omnidirectional antenna array comprising a plurality ofconductive sheet reflector structures forming the sides of a closedpolygon, each of said plurality of conductive sheet reflector structureshaving a plurality of antenna elements closely spaced thereto, each ofsaid plurality of conductive sheet reflectors being deviated in freespace wavelengths from a linear reference base eX- tending along thelength of the aperture of said antenna in direct proportion to apredetermined phase characteristic, the antenna elements associated witheach of said plurality of reflector structures by different amountsalong the length thereof in direct proportion to a predetermined currentdistribution across said aperture, and a transmission line couplingmeans common to all of said antenna elements for feeding each of saidantenna elements with equal instantaneous currents.

12. An omnidirectional antenna array comprising a conductive sheetreector forming a closed gure in cross section and having a length ofseveral wavelengths at the operating frequency and having a longitudinalaxis, a plurality of antenna elements arranged along each of a number oflongitudinal sectors, said sheet reector being deviated in distance fromthe longitudinal axis along the length thereof in direct proportion to apredetermined phase characteristic, said antenna elements in each ofsaid sectors being spaced from said reflector by different amounts alongthe length thereof in direct proportion to a predetermined currentdistribution, and transmission line means for feeding each of saidantenna elements in each sector with equal and in phase currents withrespect to the remaining elements in said sector.

llberg May 2, 1939 Cork et al. Dec. 26, 1939

